Question: $\left(-10x - 7\right)\left(-5x - 9\right) = \ ?$
Explanation: $= -10x \cdot \left(-5x - 9\right) - 7 \cdot \left(-5x - 9\right)$ $= \left( -10x \cdot -5x \right) + \left( -10x \cdot -9 \right) + \left( -7 \cdot -5x \right) + \left( -7 \cdot -9 \right)$ $= 50x^2 + \left( -10x \cdot -9 \right) + \left( -7 \cdot -5x \right) + \left( -7 \cdot -9 \right)$ $= 50x^2 + \left( 90x + 35x \right) + \left( -7 \cdot -9 \right)$ $= 50x^2 + 125x + \left( -7 \cdot -9 \right)$ $= 50x^2 + 125x + 63$